For tracking and measuring maneuvering target for video image, Extended Kalman filter (EKF) based on local linearization of KF is easy to be realized , but only has performance in Gaussian and mild nonlinear environment. An algorithm based on Unscented Kalman Filter (UKF) and Interaction Multiple Model (IMM) is proposed for maneuvering target tracking in complex nonlinearity environment or tracking small object in video image. The simulation results show that the tracking performance of UKF is much better than EKF in complex nonlinearity environment, and the third order tracking precision can be achieved.